Trivia

Before signing Joseph Losey as director, producer Seymour Nebenzal approached fellow German expatriate Douglas Sirk and offered him the job. Sirk said he would do the film only if he could scrap the original story and write a new one about a psychopathic murderer of children. When Nebenzal approached Losey, he also wanted to scrap the original story and do a new one about a child murderer, and Nebenzal told him that the Production Code Administration (PCA) had agreed to allow him to make the film only if the original story and script were kept. The PCA had approved "M" as a remake of an acknowledged classic, but if the story were changed, its approval would be withdrawn.

At 00:33 minutes, when the mobster is recruiting homeless men as lookouts, there are two signs on the alley wall behind him. The smaller, at upper left, reads: "Beware of Sneak Thieves". The large calligraphy reads: "When did you write to your mother last?". The latter was a popular choice for homeless missions of the day.

A number of actors in this film were targeted by HUAC, the House Unamerican Activities Committee, as they were known for their liberal politics. Several of the actors and crew wound up being blacklisted.

No credit is given to the classic 1931 German production (whic was directed by Fritz Lang and starred Peter Lorre) of which this film is a remake. Lang was very angry about this remake, and was savagely critical of its director, Joseph Losey, although Losey did consult him about the film before agreeing to do it.

In one scene a man insists that a little girl was wearing a blue dress while a woman insists that it was a red dress. The woman is called a "Communist". Director Joseph Losey became a victim of the Communist witch-hunts of the early 1950s.